application/x-www-form-urlencoded or multipart/form-data?

The MIME types application/x-www-form-urlencoded and multipart/form-data are the two Content-Type headers for HTTP POST requests that user-agents (browsers) must support. The purpose of both of those types of requests is to send a list of name/value pairs to the server. Depending on the type and amount of data being transmitted, one of the methods will be more efficient than the other.

Which is more suitable? http://stackoverflow.com/questions/4007969/application-x-www-form-urlencoded-or-multipart-form-data